Defining maximal outcome improvement thresholds for patient satisfaction after reverse total shoulder arthroplasty: a minimum two-year follow-up study

BackgroundPrevious research has investigated the percentage of maximal outcome improvement (MOI) for the American Shoulder and Elbow Surgeons (ASES) and Simple Shoulder Test scores after reverse total shoulder arthroplasty (rTSA); however, few other outcome scores have been validated. The purpose of this study was to establish thresholds of MOI percentage for the Single Assessment Numeric Evaluation (SANE) and subjective Constant-Murley (Constant) scores associated with patient satisfaction at 2 years following rTSA.MethodsA retrospective review of institutional registry data for all patients who underwent primary rTSA between 09/2016 and 02/2018 was performed. All patients completed the ASES, SANE, and Constant outcome measures preoperatively and at a minimum of 2 years postoperatively. Changes were assessed with Wilcoxon signed-rank tests. MOI percentage was defined as the score improvement from baseline divided by the highest possible improvement from baseline based on the maximum value of the outcome score used. Receiver operating characteristic (ROC) analyses were used to determine optimal MOI percentage thresholds associated with postoperative satisfaction. Stepwise multivariate logistic regression was performed to identify variables associated with achieving the MOI.ResultsA total of 105 patients were included in the final analysis, with a mean (±standard deviation) age of 70.0 ± 7.5 years and BMI of 28.9 ± 5.6 kg/m². The majority of patients were satisfied postoperatively (81.0%). Statistically significant increases were observed from baseline to 2 years postoperatively for the outcome measures assessed (P < .001 for all). ROC analysis demonstrated that the optimal MOI percentage threshold for achieving satisfaction was 66.9% for ASES ([Area under curve, AUC]: 0.87), 71.0% for SANE (AUC: 0.89), and 37.5% for Constant (AUC: 0.85). The linear regression model fit between the proportion of satisfied patients and the calculated MOI percentages was moderate for SANE (r² = 0.313, P < .001) and weak for Constant (r² = 0.228, P < .001). Multivariate logistic regression demonstrated that comorbid diabetes was associated with a decreased likelihood of MOI achievement for SANE ([Odds Ratio, OR]: 0.66, P = .020) and Constant (OR: 0.72, P = .027). Preoperative diagnosis of rotator cuff arthropathy (OR: 0.84, P = 0.049) was associated with a decreased likelihood of MOI achievement for Constant. No factors were significantly associated with MOI achievement for ASES.ConclusionAchieving 66.9%, 71.0%, and 37.5% of the MOI for the ASES, SANE, and Constant scores is associated with postoperative satisfaction following rTSA. Comorbid diabetes and diagnosis of rotator cuff arthropathy were significantly associated with a decreased likelihood of MOI achievement.Level of evidenceLevel III; Retrospective Case Series (Prognostic)